CN104049474A - Nano focus detection method for stacked gate stripe phase analysis - Google Patents

Abstract

The present invention provides a nano-focusing method for phase analysis of moire fringes. In the method, the optical fiber is introduced into the optical path after beam expansion in the illumination system, and the marking grating is uniformly illuminated through the condenser lens. The marking grating passes through the first telecentric imaging system, and then The image is imaged on the surface of the silicon wafer by the prism, and after being reflected, it passes through the prism, and the second telecentric imaging system; the light path is divided into two by the dichroic prism. The pattern and the target image are modulated by the detection grating, passed through the analyzer, and then demodulated by the photodetector and the circuit. The movement of the focal plane position of the silicon wafer causes the sinusoidal change of the modulated light intensity. According to the sinusoidal change of the light intensity of the two optical paths, the formula The phase change of the marked grating is obtained, and the translation amount of the marked grating image is determined, so as to obtain the change amount of the focal plane position.

Description

A nanofocus detection method based on moire fringe phase resolution

technical field

The invention belongs to grating focus detection technology in the field of projection lithography equipment, specifically relates to a nanometer focus detection method in projection lithography, and belongs to the technical field of nano device manufacturing in VLSI manufacturing and optical microfabrication technology.

Background technique

With the continuous development of large-scale and ultra-large-scale integrated circuits, the application of large numerical aperture projection lithography objective lenses and short-wavelength exposure light sources has continuously broken through the resolution of projection lithography. At the same time, in order to reduce production costs and improve production efficiency, the size of silicon wafers has been transitioned from the traditional 2.4inch (1inch=2.54cm) to 8.12inch, and even super-large-area exposure. The improvement of resolution directly leads to a sharp decline in the effective focal length; in addition, the increase in the size of the silicon wafer has brought a substantial increase in the exposure area, which leads to further deterioration of the defocus amount. At the same time, other sources of defocus error (silicon wafer Warpage, substrate topography, resist thickness, etc.) are not reduced, which makes the focus margin shrink significantly, and puts forward strict requirements for nanometer-level high-precision detection for the focus detection system.

For the situation where the accuracy of focus detection is low, most of them adopt the slit photometric focal plane detection method with a relatively simple structure and principle, which can meet the requirements of submicron level accuracy. For the focal plane detection of nanometer level, the laser Interferometric focusing technology, moire fringe method based on Talbot effect and photoelastic modulation method. Laser interferometric focusing technology cannot suppress thin-film interference caused by the silicon wafer process layer; laser interferometric focusing technology, moiré fringes of the Taber effect, and photoelastic modulation are all easily affected by the environment and the demodulation circuit at the back end is complex.

Contents of the invention

In order to solve the existing technical problems, the purpose of the present invention is to provide a simple, high-efficiency, nano-scale high-precision focusing method.

In order to achieve the above-mentioned purpose, the present invention provides a nano-focusing method for moire fringe phase resolution. The technical solution includes that the illumination system is introduced into the optical path by an optical fiber after beam expansion, and the marking grating is uniformly illuminated through the condenser lens. The marking grating passes through the first far The center imaging system is imaged by a prism on the surface of the silicon wafer, and after being reflected, it passes through the prism, and the second telecentric imaging system divides the light path into two branches through the beam splitting prism. The two light paths have the same structure, and each light path passes through the transverse shear plate. The interference pattern and the target image formed by the parallel plate are modulated by the detection grating, passed through the analyzer, and then demodulated by the photodetector and the circuit. The movement of the focal plane position of the silicon wafer causes the sinusoidal change of the modulated light intensity. According to the two optical paths Strong sinusoidal change, obtain the mark grating phase change θ, determine the translation amount ΔX of the mark grating image, and thus obtain the change amount ΔZ of the focal plane position.

Further, the light intensity distribution of the detection grating of one optical path is: I ₁ =A ₁ sin(θ), and the light intensity distribution of the detection grating of the other optical path is: I ₂ =A ₂ sin(θ+Δθ ). Among them, I ₁ and I ₂ are the obtained light intensity distribution, A1 and A2 are the AC amplitude, A1=A2; θ is the phase change of the marking grating caused by the movement of the focal plane position, and Δθ is the phase difference of the two optical paths (Δθ=90 Spend).

Further, the periods of the two detection gratings should be equal, and the period of the marking grating should be equal to the grating periods of the two detection gratings.

Further, the parallel plates of the two optical paths can adjust the phase difference Δθ of the two light beams.

Further, the second imaging system is composed of a lens, a polarizer, a photoelastic modulator assembly, and a lens.

Adopting a nano-focus detection method of moire fringe phase analysis of the present invention, the beam splitting prism divides the optical path into two branches, adjusts the parallel plate to make the phase difference of the two optical paths 90 degrees, and obtains the phase change θ of the marked grating according to the sine and cosine, Furthermore, the variation Z of the focal plane position is obtained, and the movement of the piezo stage is controlled to achieve the optimal focal plane position. Adding a photoelastic modulator component to a telecentric imaging system is equivalent to adding a high-frequency carrier, which greatly enhances the anti-interference and anti-noise capabilities of focal plane detection. The method provides high-precision, high-stability measurement accuracy and ideal measurement range through a relatively simple structure and data processing.

Description of drawings

Figure 1 is a schematic diagram of the structure of a photolithography machine;

Fig. 2 is a focus detection measurement model diagram;

Fig. 3 is a schematic diagram of the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Figure 1 is a schematic diagram of the structure of a lithography machine, in which the projection objective lens 2 projects the information on the mask 1 onto the silicon wafer 4; 3 is the nanofocus detection system, which is used to detect the best focal plane of the upper surface of the silicon wafer relative to the projection objective lens relative position. 5 is the workpiece platform for placing silicon chips.

Figure 2 is a schematic diagram of the focus detection measurement model. Using the principle of triangulation, the Z-direction displacement of the silicon wafer is converted into the lateral displacement ΔX of the marked grating image in the detection system, and the focus detection is realized by detecting ΔX.

$\mathrm{<span\; class="notranslate">\; \&Delta;X</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&Delta;Z</span>}\frac{\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}{\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}$

Where π/2-γ is the incident angle.

Figure 3 is a schematic diagram of the main structure of the focus detection system. The light output from the illumination system 1 is introduced into the optical path by the optical fiber after beam expansion, and passes through the condenser lens 2 to uniformly illuminate the marking grating 3, and the marking grating 3 image passes through the first lens composed of lenses 4 and 5. After the telecentric imaging system, the image is imaged on the surface of the silicon wafer 7 by the prism 6 (incident angle 83 degrees), and after being reflected, it passes through the prism 8 and is composed of a lens 9, a polarizer 10, a photoelastic modulator assembly 11, and a lens 12 After the second telecentric imaging system, the beam splitting prism 13 divides the light path into two branches. Adding the photoelastic modulator component 11 in the second telecentric imaging system is equivalent to adding a high-frequency carrier, which increases the anti-interference and anti-noise capabilities of the system. The two light paths divided by the dichroic prism 13 have the same structure and the same energy. One optical path passes through the transverse shear plate 131 to split the diffracted light into O light and E light whose polarization directions are perpendicular to each other, forming two sets of sinusoidally distributed light beams that are mutually misaligned, and forms interference patterns and target images through the parallel plate 132 through the detection grating 133 Modulation, through the analyzer 134, the condenser lens 135, the movement of the focal plane position of the silicon wafer 7 causes the sinusoidal change of the modulated light intensity, and then by the photodetector 136; another optical path passes through the transverse shear plate 141 to split the diffracted light into The O light and E light whose polarization directions are perpendicular to each other form two sets of sinusoidally distributed light beams that are mutually misplaced, and pass through the parallel plate 142 (adjustable phase difference, so that the phase difference of the two optical paths is 90 degrees) to form interference patterns and target images through the detection grating 143 modulation, through the analyzer 144, the condenser 145, the movement of the focal plane position of the silicon wafer 7 causes the sinusoidal change of the modulated light intensity, and passes through the photodetector 146; the light intensity change from the photodetector 136 and the photodetector 146 passes through The circuit is demodulated and sent to the PC by the AD acquisition card. According to the sine and cosine changes of the light intensity collected by AD, the phase change θ of the marked grating 3 is obtained, and the translation amount ΔX of the image of the marked grating 3 is determined, so as to obtain the change amount ΔZ of the focal plane position.

The light intensity distribution of the two optical paths is expressed by the following formula:

I ₁ =A ₁ sin(θ); I ₂ =A ₂ sin(θ+Δθ)

In the formula, I ₁ and I ₂ are the light intensity values of the two optical paths obtained by the AD digital acquisition card. A1 and A2 are AC amplitudes, A1=A2; θ is the phase change of the marking grating caused by the movement of the focal plane position, and Δθ is the phase difference of the two optical paths.

During the working process, by adjusting the parallel plate 132 and the parallel plate 142 to make a difference of 90 degrees, I ₂ =A ₂ cos(θ). Thus, the phase change of the marking grating 3 can be obtained The displacement ΔX=P*θ/2π of the picture of mark grating 3, P is the cycle of mark grating 3, and the cycle of mark grating 3 should be with detection grating 133 in the system, and the cycle of detection grating 143 should be equal. Finally, according to the principle of trigonometry, the change ΔZ of the focal plane position is obtained.

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone familiar with the technology can understand the conceivable transformation and replacement within the technical scope disclosed in the present invention. All should be covered within the scope of the present invention.

Claims (5)

1. the nanometer focusing test method of a Moire fringe Phase-Resolved Analysis, it is characterized in that: the method comprises that according to the direction of propagation of incident light illuminator introduces light path by optical fiber after expanding, through condenser Uniform Illumination mark grating, mark grating is through the first telecentric imaging system, again by prism imaging at silicon chip surface, after being reflected through prism, the second telecentric imaging system; By Amici prism, light path is divided into two, two light channel structures are identical, every light path is all passed through Transverse Shear cutting plate, and parallel flat formation interference pattern and target picture are by detecting Grating Modulation, through analyzer, again by photodetector and circuit demodulation, the movement of silicon chip position of focal plane causes modulation light intensity generation sinusoidal variations, according to the sinusoidal variations of two light path light intensity, obtains mark raster phase and changes θ, determine the translational movement Δ X of mark grating image, thereby obtain the variation delta Z of position of focal plane.

2. the nanometer focusing test method of a kind of Moire fringe Phase-Resolved Analysis according to claim 1, is characterized in that: the light distribution of the detection grating of a light path is: I ₁=A ₁sin (θ), the light distribution of the detection grating of another light path is: I ₂=A ₂sin (θ+Δ θ), wherein I ₁, I ₂for the light distribution obtaining, A1, A2 is for exchanging amplitude, A1=A2; θ is that the phase place variation that causes mark grating is moved in position of focal plane, and Δ θ is the phase differential of two light paths, Δ θ=90 degree.

3. the nanometer focusing test method of a kind of Moire fringe Phase-Resolved Analysis according to claim 1, is characterized in that: two cycles of detecting grating should equate, and the cycle of mark grating should equal the grating cycle of two detection gratings.

4. the nanometer focusing test method of a kind of Moire fringe Phase-Resolved Analysis according to claim 1, is characterized in that: the phase difference θ of adjustable two light beams of parallel flat of two light paths.

5. the nanometer focusing test method of a kind of Moire fringe Phase-Resolved Analysis according to claim 1, is characterized in that: the second imaging system is by lens, the polarizer, and light ball modulator assembly, lens form.